Purification of hydrocarbons



Feb, 279 i951 J. w. TooKE Erm.

PURIFICATION oF HYDRocARBoNs Filed May 7, 194e NOLLVNOLLDVHJ mozr z AINozi m. moz:

Patented Feb, 21, 1.951

James w. Tooke, Bartlesville, ons., and PaulF. Warner, Phillips, Tex.,assiznors to Phillips Petroleum Company, a corporation of Delaware 'lApplication May 7, 1946, Serial N0. 667,790

11 Claims. (Cl. 202-57) This invention relates to purification ofhydro,- carbons and more particularly to treatment of 'hydrocarbonscontaminated with acetylene hydrocarbons to remove such acetylenehydrocarbons. More specically it relates to a process o1' removinghomologues of acetylene (C2H2) from aliphatic C3 to C4 hydrocarbons atleast as saturated as a dioleiln, i. e., either \diolens, oleiinsorparalns. Still more speciiically it relates to a `process of removing aC4 acetylene hydrocarbon impurity from butene-2 in order to makeavailable to the art butene-2 ci extreme purity suitable, for example,for the calibration of analytical and control instruments used in plantprocess operation especially in the aviation gasoline and syntheticrubber industries.

Contamination of hydrocarbons with homologues of acetylene -is a veryserious problem, especially in the manufacture of light hydrocarbonsespecially the aliphatic C3 and C4 parafilns, oleflns and dioleflns.These acetylene hydrocarbon impurities appear to be formed as the resultof side reactions which accompany the productionl of oleiins and'diolefins by catalytic and thermal (non-catalytic)A methods. Theacetylene impurities boil in the same range as the Ca-and C4hydrocarbons with which they are associated, and by reason of theirclose-boiling point and/or tendency to form azeotropes with the C3 andC4 paraiins, oleiins and diolens, it is extremely diiiicult orimpossible to separate them by conventional means such asJ fractionaldistillation, rextractiva distillation or the like. For example, 'thesolvents which are selective for the olefin and/or dioleiins appear tobe even more selective for the vacetylene hydrocarbons with which ourinvention is/concerned.

Prior to ourA `vention, it Vwas impossible to produce butene-2 hich wassufiiciently free from acetylenes to" enable its use for the calibrationof instruments such as spectrophotometers used inthe aviation gasolineand synthetic rubber'industries. Our invention provides a simple,economicalA and certain method of producing butene-2 of this extremepurity.

The acetylene hydrocarbons dealt with in ac- 2 The hydrocarbons whichmay be present in mixtures treated in accordance with our invention maybe listed as follows, together ,with boiling point:

. y N ormai Hydrocarbon Bodini` Point,

Propylene. 53. 9 Proplane. l 43. 7 Met yi Acetylene -9. 6 Isnhnta'na+10, 9 Isobutylerm 19. 6 Butene-l.-- 20. 7 Butadene-l, 'i 24. l N-Butann31, 1 Butene-2 (trans) 33. 6 Butene-2 (cis) v 38. 7 Vinyl acetylene 4l.2 Ethyl acetylene 47. 8 Baeetlane I 1 49. 6 Dimet yl acetylene 8/l.,0

cordance with-our invention are predominantly or exclusively the Ca andC4 acetylenes. Ordinarily in a C3 stream a Cz acetylene is encounteredwhile in a C4 stream the C4 acetylenes are present.

It was shown in Walls et al. 2,371,860 that methyl acetylene and propaneform an azeotrope of the minimum-boilingtype. The existence oi' anazeotrope between propylene and methyl acetylene is in doubt. It wasshown in Buell 2,382,603 that minimum-boiling point azeotropes existbetween vinyl acetylene and butenes-Z and between ethyl acetylene andbutenes-Z.V It is also reliably reported that vinyl acetylene and ethylacetylene form azeotropes with other C4 hydrocarbons, particularlynormal butane and isobutane. Resolution of such azeotropes by knownprocedures is very difcult or imposible.

Hydrocarbons containing an acetylenic linkage are very undesirableimpurities in butadiene that is to be used as an intermediate forchemical synthesis or in rubber synthesis. Specifications for butadieneto be used in rubber manufacture are very strict with respect toactelyenes content. Separation of methyl acetylene from butadiene hasbeen a serious'problem. It has been proposed in the copendingapplication of Hachmuth Serial No. 480,084, led March 22, 1943, now U.S'. Patent 2,434,923, issued January 27, 1948, and of Dean Serial No.654,439, filed March 14, 1946, now U. S. Patent 2,486,929, issuedNovember 1, 1949, to eilect this separation in the same fractionaldistillation column wherein butadiene is separatedv from butenes-2.However this separation requires .the use of an expensive fractionationcolumn. Furthermore, the operation of such a column may become upset forvarious reasons, allowing production of a product .which contains toomuch methyl acetylenes to pass specifications. Our invention provides aninexpensive and positive chemical method of effecting the separation ofmethyl acetylene from butadiene.

The presence of acteylenic impurities in light hydrocarbon streams fedto conversion processes such as alkylation, isomerization.polymerization, etc.. is often highly undesirable and cannot betolerated. For example, the normal butane fed to a process in which itis isomerized to isobutane with an aluminum chloride catalyst must beabsolutely free from acetylenes. Similarly the isobutane and ethylenefed to a process for the manufacture of diisopropyl by alkylation usingan aluminum chloride-hydrocarbon complex catalyst must be free fromacetylenes.

The principal object ofl our invention is to provide an improved methodof removing homologues of acetylene from hydrocarbons. Another object isto provide a simple, economical and positive method of removing suchacetylene hy drocarbons from aliphatic Cs to C4 parafiins, oleilns anddioleilns. Another object is to provide an improved method of removingacetylene hydrocarbons from butene-Z.V Another object is to provide amethod of making butene-Z of extreme purity suitable for calibration ofanalytical and control instruments, such as spectrophotometers, used inthe processing of light hydrocarbon streams especially Ca to C4hydrocarbons at least as saturated as a diolefln for the manufacture ofaviation gasoline and synthetic rubber components. Numerous otherobjects will be apparent to those skilled in the art from the foregoingdiscussion and the following disclosure.

The accompanying drawing portrays diagrammatically one arrangement ofequipment which is very suitable for the practice of our invention. Inaccordance with our invention acetylene hydrocarbon impurity is removedfrom an aliphatic hydrocarbon contaminated therewith by intimatelycontacting said hydrocarbon with an aqueous acidic solution of amercuric compound, said solution also containing a lower saturatedaliphatic alcohol, under conditions such that the acetylene hydrocarbonimpurity is converted to ketone by reaction with water, the acidicmercuric solution acting as a catalyst. The hydrocarbon is thenseparated from the ketone in any suitable manner.

The contacting of the hydrocarbon with the reagent solution ispreferably conducted with the hydrocarbon in the gaseous phase in themanner known in the art as gas scrubbing. For example, the vaporizedhydrocarbon feed is introduced into the bottom of a vertical gas-liquidcontacting unit and allowed to ascend therein and simultaneously beintimately washed or scrubbed with the aqueous reagent solution. Meansof any suitable type may be provided for increasing the intimacy ofcontact. For example, bubble trays, baiiies. perforated trays, packingor the like may be provided within the scrubber. 'I'he scrubbing shouldbe carried out in such manner that the desired degree of acetyleneremoval is accomplished during passage of the gas therethrough.

While we highly prefer gas-liquid contacting, we do not wish completelyto exclude liquid-liquid contacting. Under some conditions it may befeasible to have the hydrocarbon in the liquid state during thecontacting. However, it may 4 be diflicult to prevent reaction betweennon acetylene hydrocarbons in the feed, such as olefins or dioleflns andthe reagent if the hydrocarbon feed is in liquid phase. As will appearmore fully below. it is imperative that conditions of treatment are suchthat no auch reaction takes place. i

The temperature of the scrubbing operation should be such that. underthe otherconditions employed. principally pressure, reaction between thenon-acetylenic components of the hydrocarbon feed and the reagentsolution is substantially or completely prevented. 'Ihis practicallyamounts to a requirement that elevated temperature be employed since atsuch temperatures the equilibrium between oleilns or dioleiins andmercuric salts is such that practically no reaction can occur.Furthermore we have found that the use of elevated temperatures preventsor retards formation of a precipitate in the scrubbing zone. As willappear more fully hereinafter, the formation of such a precipitate is`4highly undesirable because it represents a spending of the catalystsolution and requires the consumption of chemicals to counteract it.

'I'he temperature at which the scrubbingis conducted may vary widely.Temperatures of at least F. are ordinarily employed. In the purificationof butene-2 in accordance with our invention we have found a temperatureof from to 160 F. to be preferable.

Ordinarily the scrubbing zone will be provided with any suitable meansfor maintaining the required elevated temperature. This may take theform of an electrical heating coil wound around the scrubbing zone whereit is small or heating coils disposed within /the scrubbing zone. Insome cases enough heat to maintain the desized temperature mfay besupplied by suitably preheating the hydrocarbon feed and insulating thescrubbing zone to prevent loss of heat therefrom.

Any aqueous acidic solution of any mercury compound may be employed.However. we prefer to use mercuric sulfate in solution in sulfuric acid.The sulfuric acid is ordinarily quite dilute, ranging from 2 to 'Iweight per cent of HzSOi based'on the total weight of the solution.

The concentration of mercuric (Hg++) ion in the treating solution mayvary within very wide limits. Ordinarily we prefer to use from 0.5 to 5weight per cent of mercuric sulfate based on total weight of thesolution. The minimum concentration of mercuric ion for satisfactoryoperation depends upon so many variable factors that it cannot bespecified definitely; however, it is very low.

The gas issuing from the scrubbing operation comprises the hydrocarbonand the ketone. The hydrocarbon of greatly reduced acetylene content isseparated from the ketone in any suitable manner. usually by simplefractional distillation. Usually this gaseous material leaving thescrubber contains some alcohol volatiiized from the treating solution byreason of the elevated temperature. Apparently an azeotrope of thehydrocarbon and alcohol goes overhead in the distillation in some cases,at least. We prefer to remove such alcohol from the product hydrocarbonby washing the overhead fraction from the fractional distillation stepwith water. The resulting hydrocarbon may be dried if desired andconstitutes the product of our invention.

An essential feature of our invention is the presence of substantialquantities of a lower saturated.l aliphatic alcohol, preferably one'having not more than two carbon 4atoms perumolecule, namely. methylalcohol or r`ethyl y alcohol, in the treating solution. The amount ofsuch alcohol. may vary within extremelywide limits but ordinarily willrangeffrom 'l to 20-weight per cent of the solution. p

The .alcohol markedly reducesthe tendency oi the treating solution `toform precipitates. The alcohol also greatly reduces frothing and foamingof the scrubbing solution, apparently by reduclng the surface tension.'Ihe most troublesome problem connected with the use of an acidicmercury solution to remove acetylene hydrocarbons is that of keeping themercury salt catalyst insolution. Even when alcohol is used'there isalways some precipitate formed and it has been found to be a mixture vofmetallic mercury and mercury salts. It was found that the solution couldbe regenerated periodically Vby withdrawing theprecipitate'from thebottom of the scrubber or reactor, redissolvmg it 1n concentrated niticl acid and returning the resulting solution to the elevated temperatureof operation (usually 140 to.

160 F.) sothat it is also necessary to add alcohol at infrequentintervals.

Methanol is preferable to ethanol because it is readily availablein'commercial grade and seems to bethe equivalent of or betterthanethanol in everyA respect.

After the process was set up on pilot plant or plant scale, it was foundpossible to use the solution indefinitely by the use of alcohol andnitric acid as described above. Y

The amount of water in the treating solution will generally be at least70 per cent by weight and may range upwardly therefrom to any desiredligure.-

It is often preferred to use ferric sulfate in substantial proportion inthe treating solution.v This functions principally as an indicatoralthough it also appears to prevent the precipitation of` mercury. Whenferric sulfate is present, as long as the solution is yellow, it isknown with ce1'- tainty that the addition of nitric acid or of mercuriccompound is unnecessary. When the solution turns green, indicating thepresence of ferrous iron, the addition of nitric acid and of mercuricsalt` is necessary. p v

The pressure maintained infthe scrubber may where` even the slightesttrace 'of acetylenes would be objectionable. It is thereforeclear thatby suillcientlythorough or repeated application of the principles of ourinvention it is `possible to completely freethe hydrocarbon from anyde.- tectable amount of acetylene hydrocarbon im- Pure low-boiling ofour invention is being used as a standard for the calibration of thespectrometers used throughout this country as control instrumentsinthesynthetic rubber and aviation gasoline industries. 4 l

`Inl the drawing-.the hydrocarbon containing acetylenic hydrocarbonimpurity entersv v the system via line ;I.- If it is in liquid form orif it is desired that additional kheat Abe imparted to the gaseoushydrocarbon prior to entering thescrubbing step, it is passed throughheater 2 where it is brought to any suitable elevated temperature as forexample 140 to .160 F. It is then passed into scrubber 3 which ispreferably a lagged vertical tower provided with plates 4 or any othersuitable means for promoting intimate contact between gas and scrubbingliquid. Scrubbing liquid is introduced to the scrubber initially via bevaried over wide limits. Ordinarily the `pressure is such that thehydrocarbon being treated is in the gaseous phase. It will be understoodthat the pressure should be such that the reaction of oleilns or diolensin the hydrocarbon with the mercuric salt is prevented. vThe pressurewill or- Mdinarily be only' moderately in excess of supersuchcompleteremoval by the practice of our invention that theproduct hydrocarbon issuitable `for the calibration of spectrophotometers line 5. If desiredthe scrubbingpliquid may be withdrawn land recirculated continuously vialines 6, 1 and 8. Any precipitate reaching the bottom of the scrubber 3may be withdrawn via line 9 and either discarded via. line I0 or passedto step Il wherein it is dissolved in concentr ted HNOa, the resultingsolution being returne `t0 the scrubber `3 via lines i2, i3 and 8.Alcohol ay be added to the system via line I4 as neede I to make upsystem losses. Mercuric nitrate may be added via line I5. N tric acidmay be added as necessary via line l' If during operation it is desiredto add fresh sulfuric acid solution of mercuric sulfate, this may beintroduced via line 5. The gaseous mixture of the hydrocarbon and theketoneleaves scrubber 3 via line I1 and is liquefied by passage throughcondenser i8. If desired, compression by compressor I9 may also beemployed to aid in eiecting the liquefaction. The liquid mixture is thenfed to fractional distil:

- lation column 2l) which is operated at any suitable conditions ofpressure and temperature and separates the feed into an overhead of thehydrocarbon and some alcohol and a bottoms product of the ketone. Theoverhead is preferably waterwashed in unit 2| to give the purehydrocarbon product which is withdrawn via line 22.

vExample l Product HgSOA 1 Hiso. l 173 H30 50 Methanoll0 HNO: andHg(NO3)z were added at infrequent intervals to regenerate the catalystand keep Hg++ concentration at the desired level. Ninetynine plus percent conversion wasl easily obtained when operating conditions wereright.`

The reaction vessel was a 3" x 6 joint of Pyrex pipe with an externalelectrical heating coil butene-z prepared :by ,means asians wound on it.The volume of solution varied from 5000 to 6000 ml. in the reactionvessel. A pressure of 20 to 25 pounds per square inch gage wasmaintained. Flow rates varied from l# to 2# per hour of butene dependingon the percentage of acetylene present. The butene2 was charged from onepressure cylinder through the reactor and collected in a receivercylinder. The butene2 was freed of ketone and methanol by subsequentfractionation.

The acetylene hydrocarbon impurity in the butene2 was found by infra-redspectrophotometrlc analysis to be a four carbon atom acetylene andundoubtedly was ethyl acetylene. The ketone formed during thepurification was identified by boiling point, specific gravity andrefractive index as being methyl ethyl ketone.

Example Il Run I Run II Solution Composition:

.gram5 25 25 .-do. 25 26 |0 ml-- l, 900 l, 900 HISOKGG B6.) ml-. 25 25CHsCHgOH ml-. 0. 0 200 Total liquid volume cf hydrocarbon through beforediscarding mi. im 1,100 Aeeiylene in product at end of run. pcr cent. 0.43 0. 2G Average Acetylene in Product do. 0. 23 0. U5

Example II clearly illustrates the marked advantages of using methyl orethyl alcoholin the catalytic solution.k

From the foregoing detailed description a great many advantages of ourinvention will be apparent to those skilled in the art. The principaladvantage of course is that the invention provides a simple andeconomical way of removing acetylenichydrocarbons from' aliphatichydrocarbons contaminated therewith. The method is positive. Thechemical consumption is low if the precipitate formed is redissolved andreturned in the manner described. The method is easily carried out. Theequipment requirementsare low. If desired the ketone or ketones producedmay be recovered and sold as a by-product. AOne of the most importantadvantages is that the invention solves a problem which had notheretofore been solved, namely the problem of complete removal ofacetylene hydrocarbon impurities from research and calibration gradehydrocarbons such as the butylenes and especially butene2.

We claim:

1. 'I'he method of effecting the removal of a C4 acetylene hydrocarbonimpurity from butene2 which comprises passing said butene2 as a vapor infine dispersion through a catalyst solution of approximately thefollowing composition in parts by weight: HgSO4 l, H2804 1-3, water 50,methanol 10, maintaining said solution at a temperature of from 140 to160 F., periodically addini HNO: and Hg(NOs)z to regenerate the cat- HgO25 Fez(SO4)s 25 Water 1800 H2804 43 Ethyl alcohol 158 maintaining saidsolution at a temperature of approximately 150 F.. thereby convertingsaid C4 acetylene hydrocarbon to a ketone, a precipitate of metallicmercury and mercury compounds forming duringv said contacting,regenerating said solution by withdrawing said precipitate from thecontacting zone, dissolving said precipitate in concentrated nitric acidand returning the resulting solution to the contacting zone, addingethyl alcohol as needed to replace that escaping in the oil-gas,withdrawing a resulting gaseous mixture of butene2, ketone and someethyl alcohol from the contacting zone, fractionally distilling saidm.xture to separate it into an overhead fraction of butene2 and ethylalcohol and a bottoms fraction of said ketoneand waterwashing saidoverhead to recover the butene2 free of alcohol.

3. 'ihe process of purifying on a continuous basis a butene2 streamcontaining acetylenic compounds as impurities in a proportion below 5per cent by weight, which comprises passing such a. butene2 stream inthe gaseous state to the lower portion of a contacting zone andcontacting same therein in counter-current flow with an acidic aqueoussoltuion of a mercuric salt containing free nitric acid and an aliphaticalcohol having not more than two carbon atoms in the molecule at atemperature in the range of 140 to 160 F. at a pressure of at leastatmospheric, a precipitate of a mixture of metallic me"cury and mercurycompounds forming during said contacting, continuously withdrawing saidprecipitate from the contacting zone and dissolving same in nitric acid,admixing a resulting nitrate solution therefrom with a lower aliphaticalcohol having not more than two carbon atoms per molecule and passingthe resulting admixture to said contacting zone, continuouslywithdrawing gaseous effluent from the upper portionof said contactingzone and passing same to a fractionation step, and recovering therefrombutene2 substantially completely free of acetylenic impurities as aproduct.

4. The process of claim 3 wherein the contacting solution in saidcontacting zone contains on a weight basis at least per cent'water, 'lto 20 per cent methyl alcohol, 2 to 7 per cent sulfuric acid and from0.5 to 5 per cent mercuric salt.

5. In a method for purification in vapor phase of butenes containingacetylenic hydrocarbon impurities having four carbon atoms per moleculeand in a concentration below 5 per cent by weight, the improvementcomprising continuously eilecting a removal of such an impurity at atemperature above 100 F. and not higher than `i60 F., by contacting sucha butene in countercurrent ow with an aqueous acidic solution of amerc-uric salt while simultaneously maintaining a constant concentrationof mercurio ions in said aqueous solution by the continuous additionthereto of an admixture of nitric acid, mercurio nitrate, and aloweraliphatic saturated alcohol having not more than two carbon atomsper molecule in such an amount as to maintain said aqueous solution.

6. In a method for purification of butenes containing acetylenichydrocarbon impurities having four carbon atoms per molecule and in aconcentration below per cent by weight, the improvement comprisingcontinuously effecting a removal of such an impurity at a temperatureabove 100 F. and not higher than 160 F., at a pressure of at least oneatmosphere, by contacting such a butene in countercurrent ow with e.dilute aqueous acidic solution of from 0.5 to 5 per cent mercuriosulfate, mercurio nitrate, 2 to '7 per cent sulfuric acid, nitric acidand from 7 to 20 per cent of an aliphatic alcohol containing not morethan two carbon atoms in the molecule while simultaneously maintaining aconstant concentration of mercuric ions in said aqueous solution by thecontinuous withdrawal of aqueous solution from the zone of saidcontacting and the continuous addition thereto of an admixture of alower aliphatic saturated alcohol having not more than two carbon atomsper molecule and mercurio oxide dissolved in nitric acid, and addingsaid admixture in an amount as to maintain the concentration of mercurioions in said aqueous solution.

'7. The method of claim 5 wherein said alcohol is methanol.

8. The process of purifying a predominantly Cs-Ci aliphatic hydrocarbonmixture containing acetylenic impurities, which comprises contactingsuch a hydrocarbon stream in a contacting zone in countercurrent flowwith an acidic aqueous solution of a mercurio salt at a temperature inthe range of 140'to 160 F. at a pressure of atleast atmospheric, aprecipitate of a mixture of metallic merc/u'ry and mercury compoundsforming during said contacting, continuously withdrawing saidprecipitate` from the contacting zone and dissolving same in nitricacid, admixing a resulting nitrate solution therefrom with a loweraliphatic alcohol having not more than 2 carbon atoms per molecule andpassing the resulting mixture to said contacting zone, continuouslywithdrawing gaseous eiiluent from the upper portion of said contactingzone and passing same to a fractionation step, and recovering therefromas a product of the process a Cs-C4 aliphatic hydrocarbon mixturesubstantially free of acetylenic impurities.

9. The process for purifying a normally gaseous aliphatic hydrocarbonmixture containing acetylenic impurities, which comprises contactingsuch a hydrocarbon stream in a contacting zone in countercurrent flowwith an acidic aqueous solution of a, mercurio/salt containing freenitric acid and from '7 to 20 per cent of an alcohol having not morethan two carbon atoms in the molecule at a temperature in the range of140 to 160 F. at a pressure of at least one atmosphere, a precipitate ofa mixture of metallic mercury and mercury compounds forming during saidcontacting, continuously withdrawing said precipitate from thecontacting zone and dissolving same in nitric acid, admixing a resultingnitrate solution therefrom with a lower aliphatic alcohol having notmore than 2 carbon atoms per molecule and passing the resulting mixtureto said contacting zone, continuously withdrawing gaseous eliuent fromthe upper portion of said contacting zone and recovering from thewithdrawn eilluent as a product of the process a normally gaseousaliphatic hydrocarbon mixture substantially free of acetylenicimpurities.

10. In a process wherein a butene-2 stream containing acctyleniccompounds as impurities in a proportion below 5 per cent by weight ispurified by passing same in the gaseous state vin countercurrent flowreation with an acidic aqueous solution of a mercurio salt at atemperature within the limits of 140 to 160 F. at substantiallyatmospheric pressure, and wherein a precipitate of a mixture of metallicmercury and mercury compounds forms during said countercurrent ow, theimprovement comprising withdrawing said precipitate and dissolving samein nitric acid, admixing a resulting nitrate solution with an aliphaticalcohol having not more than two carbon atoms per molecule, and passingthe resulting admixture to the zone of said countercurrent contacting,whereby the concentration of mercury ions in said zone of countercurrentcontacting is maintained at a constant level.

11. In a process for the purification of butenes containing acetylenichydrocarbon impurities in a concentration below 5 per cent by weightwherein such a butene stream is passed in the gaseous state incountercurrent flow relation with a dilute aqueous acidic solutioncontaining from 0.5 to 5 weight per cent mercurio sulfate and from 2 to7 per cent by weight c* sulfuric acid, at substantially atmosphericpressure and at a temperature within the limits of 140 to 160 F., andwherein a precipitate of a mixture of metallic mercury and mercurycompounds forms during said countercurrent ow, the improvementcomprising the dissolving of mercurio oxide in nitric acid andintroducing the resulting nitrate solution together with an aliphaticalcohol containing not more than two carbon atoms in the molecule intosaid zone of countercurrent contacting in an amount such as to maintainthe concentration of mercurio ions in said aqueous solution.

JAMES W. TOOKE. PAUL F. WARNER.

REFERENCES CITED The following references are of record in the v ille ofthis patent:

UNITED STATES PATENTS Date

10. IN A PROCESS WHEREIN A BUTENE-2 STREAM CONTAINING ACETYLENICCOMPOUNDS AS IMPURITIES IN A PROPORTION BELOW 5 PER CENT BY WEIGHT ISPURIFIED BY PASSING SAME IN THE GASEOUS STATE IN COUNTERCURRENT FLOWRELATION WITH AN ACIDIC AQUEOUS SOLUTION OF A MERCURIC SALT AT ATEMPERATURE WITHIN THE LIMITS OF 140 TO 160* F. AT SUBSTANTIALLYATMOSPHERIC PRESSURE, AND WHEREIN A PRECIPITATE OF A MIXTURE OF METALLICMERCURY AND MERCURY COMPOUNDS FORMS DURING SAID COUNTERCURRENT FLOW, THEIMPROVEMENT COMPRISING WITHDRAWING SAID PRECIPITATE AND DISSOLVING SAMEIN NITRIC ACID, ADMIXING A RESULTING NITRATE SOLUTION WITH AN ALIPHATICALCOHOL HAVING NOT MORE THAN TWO CARBON ATOMS PER MOLECULE, AND PASSINGTHE RESULTING ADMIXTURE TO THE ZONE OF SAID COUNTERCURRENT CONTACTING,WHEREBY THE CONCENTRATION OF MERCURY IONS IN SAID ZONE OF COUNTERCURRENTCONTACTING IS MAINTAINED AT A CONSTANT LEVEL.